Given that this is a USDA resource I really thought that it would be available online somewhere, but for the life of me I cannot find a shapefile for the USDA plant hardiness zones anywhere. Does anyone know where there might be one?

This link is the closest I found but it doesn't seem to offer any sort of shapefile download:

Have you looked here http://www.hardiness-zone-map.com/?
The map is implemented with overlays on Google maps. If you read the script that implements the map, you can find where the .png files are located. Not a pretty solution, but it might work.

yes I did find this site, but I thought that as a USDA resource that this would really would be available online somewhere, and being able to work with the shape file would certainly be easier than scraping the URLs off this site-
– chrismarxJan 5 '12 at 2:45

I looked into using the annual mean minimum temperature a bit more, and it's not clear to me what is the official way to calculate the hardiness zones. According to wikipedia (perhaps not the best reference...) the mim summer month temps are not used (en.wikipedia.org/wiki/Hardiness_zone), while the metadata link in the other answer indicates that perhaps it is based on all the months. Unfortunately, I really need some official file here, because I don't want to accidentally tell people they're in the wrong zone, because the process I followed is different from the USDA's
– chrismarxJan 5 '12 at 15:26

The National Arboretum site you listed in the question describes the zones as average annual minimum temperature in the legend. I think that's the same as the contents of the climate data link.
– LlavesJan 5 '12 at 15:43

If you compare the map on the national arboretum site to the one at the noaa site, you'll notice vast differences. I'm hoping someone will email me from one of the several places I contacted, and I will definitely try put this resource on a public host-
– chrismarxJan 5 '12 at 16:03

I think this is probably the best direction to be taking... I know this question is old, so has anyone had luck finding a good shapefile for the average minimum temperature?
– thegreyspotMar 14 '13 at 18:39

Here is a link to a same question as yours in Google+, and with an explanation from "The Agricultural Research Service (ARS) of the U.S. Department of Agriculture", with reasons why data can't be freely available.

Follow the posts of a woman named "Jeanne Holm". In her third post (Jan 12th, first paragraph) she says:

The issue in releasing that data is that USDA does not actually own the rights to release the data in its machine readable format beyond the government.

her post contain the extended answer directly from USDA

In the third paragraph she presents a solution of short-term to the guy who made the question ("Michael Bernstein"). See if it helps you.

The short-term solution is that I could extract the individual tables from the paper referenced below and load those into Data.gov. And I can do that if it will be helpful. The long-term solution is to liberate data that is gathered or created by the government under the emerging policy changes you can see at the White House Open Data Initiatives that Data.gov is part of: http://www.whitehouse.gov/innovationfellows/opendata and http://project-open-data.github.com/ We are working aggressively to make this happen. Stay tuned.

New discussions started (October, 22th, 2013) on the same Google+ thread and maybe some changes can come in the future.

If you search around for a bit, you'll find some online hardiness maps but all the ones I've seen look like they're just raster overlays. I've also seen some states that have digitized their hardiness maps (I've seen Idaho's and Montana's), so if you happen to need a limited dataset and are fortunate about which state you need it from, you might be in luck.

Hi, Even a decent raster would be ok, I could use that or convert it to a vector file. I do however need it for the whole US. The link you posted does seem to point to the resource I'm looking for, but I don't see any place to download that resource on the climatesource site. Did you see it available for download?
– chrismarxJan 5 '12 at 1:57

I didn't see it available for download, but the metadata did have contact information so you could try that route. Good luck!
– Jason BakerJan 5 '12 at 3:00